(1) Field of the Invention
The present invention relates to a mobile electric flash-butt welding machine for welding together adjacent ends of successive rail sections of a rail of a track consisting of two rails fastened to successive ties, which machine comprises machine frame, undercarriages supporting the machine frame on the track for mobility therealong in an operating direction, and a drive for propelling the machine frame along the track. The machine frame carries a hydraulic fluid supply pump means, an electric current generator, motor means for operating the pump means and the generator, and a longitudinally, transversely and vertically adjustable electric flash-butt welding head for selectively welding together the adjacent rail section ends of a respective one of the track rails. The welding head comprises two welding head halves movable towards and away from each other in a direction of the rail, hydraulic cylinders for moving the two welding head halves in this direction, a pair of clamping and welding jaws on each welding head half, a hydraulic clamping cylinder connecting the jaws of each pair, and optionally a hydraulically operable welding seam shearing device. A welding control connects the pump means and generator to the hydraulic cylinders and jaws respectively for hydraulically and electrically operating the clamping and welding jaws.
(2) Description of the Prior Art
A mobile flash-butt welding machine of this type has been disclosed in the Plasser & Theurer prospectus K 355 APT, of February 1986. In this machine, the generator for supplying electric current to the welding jaws and the control box are mounted on the machine frame between two operator's cabs arranged at the front and rear ends of the machine frame. One of the cabs is longitudinally displaceable and has an open end for accommodating a double-arm telescopic jib crane pivotal about a vertical axis on the machine frame. The welding head is vertically adjustably suspended from a free end of the crane and the crane movements are powered by hydraulic cylinders. When the cab is retracted, the crane can turn 90.degree. with respect to the center axis of the machine frame, the center of the welding head being adjustable up to 3250 mm from the center of the track. When the machine is moved between operating sites, the crane is retracted through the open end into the cab, the cab is longitudinally displaced to the end of the machine frame and the open end is closed. A respective pair of clamping and welding jaws for engaging the rail web therebetween is arranged at the underside of each welding head half, and these jaws serve not only to clamp the rail but also conduct the electric welding current. The hydraulic clamping cylinders are connected to mechanical lever systems on each welding head half for pressing the jaws into engagement with the rail web. The welding head carries a control panel for initiating and ending the welding operation as well as for the control thereof.
In the method of providing an electric flash-butt joint between adjacent ends of successive rail sections of a rail of a track consisting of two rails fastened to successive ties, the welding machine is moved to the operating site and after the welding head has been lowered and centered over the gap between the adjacent rail sections ends to be welded together, the successive rail section ends ahead and behind the joint are clamped by the two pairs of clamping and welding jaws. At the same time, the clamped rail section ends are accurately leveled and lined. The "automatic" operating switch is then actuated for the programmed welding operation. In the initial stage, the two hydraulic cylinders are operated to move the two welding head halves with the rail section ends clamped thereto towards each other at an approximate speed of 0.25 mm/second until the two ends touch. Upon contact of the rail section ends and the resultant short circuit, the welding current reaches its first peak value. As soon as the control including a current measuring device senses this, the movement of the two welding head halves towards each other is stopped while the temperature of the two rail section ends rises sharply. After about a second, the two welding head halves are moved apart, causing the two rail section ends to be torn apart again and their temperature to be lowered, which instantly iniates the movement towards each other. This to-and-fro movement is repeated several times, the temperature of the two rail section ends increasing progressively. When the temperature at the contact between the two rail section ends has reached a critical point, a welding melt occurs. After about 30 seconds of this unstable welding phase, the progressive heating of the welding joint leads to a stable welding phase during which the two rail section ends are moved towards each other at a constant speed. After a pre-selected welding time has passed, the progression phase is initiated. Within about ten seconds, the speed of the movement is tripled or quadrupled, causing a corresponding increase in the current density and raising the welding temperature to its maximum. The welding current is now discontinued and the clamping and welding jaws are held in position. A hydraulic fluid flow control valve is now operated to increase the hydraulic fluid flow to the cylinders to move the two rail section ends together at a rapid pace in a final compression stage so that the rail section ends are pressed together at a set value. The movement is then discontinued while the clamping and welding jaws hold the welded rail section ends in position for a few seconds until the welded joint has cooled off a little. Afterwards, the clamping and welding jaws are released, the welding head halves are retracted while two weld seam shearing knives are closed and the welding head halves are moved together again to shear off the welding seam. The clamping and welding jaws as well as the shearing knives are then opened, and the welding head is lifted off the welded rail. The machine is now ready for movement to the next operating site.
This machine and various operating modes thereof are also described in great detail in the October 1977 issue of "Railway Gazette".
U.S. Pat. No. 3,349,216, dated Oct. 24, 1967, discloses an electrically operated flash-butt welding head useful in rail welding operations, which comprises two welding halves displaceable with respect to each other and designed to clamp the adjoining rail sections and pull them together. The rail clamps constitute welding elements and have a common rotary axis wherealong they are displaceable by means of hydraulically operated cylinders. The piston rods of the operating cylinders connect the clamps and are arranged symmetrically with respect to the weld and are coplanar therewith. The rotary axis is constituted by a hollow rod containing a control valve for uniformly delivering hydraulic fluid to the operating cylinders and the control valve is actuated by an electromagnetic drive mounted on the rod.
British patent No. 1,513,014, published June 1, 1978, also discloses an electric flash-butt welding head with clamping and welding jaw pairs for engaging a rail web by means of a lever system operable by a clamping cylinder. A welding seam shearing device comprises four shearing knives which completely encompass the profile of the rail in their operating position. Such a welding seam shearing device incorporated into the welding head makes it possible to use the same without any auxiliary equipment.
The welding machine disclosed in U.S. Pat. No. 4,272,664, dated June 9, 1981, provides a hydraulic support shoe for the machine frame to relieve the track rails of the machine weight before the welding. The thus relieved rail may then be slid more readily to reduce the welding gap.
The flash-butt welding heads in these machines exert a sufficient tensioning force on the rail sections to enable short rail sections to be welded together or to weld together longer rail sections if they are supported on rollers to reduce frictional resistance to a minimum. In end welds, the rails are lifted out of their fastening elements and changes in the rail length due to welding are compensated for by inserting corresponding lengths of rail section. However, a relatively large tensioning force is required to provide flash-butt welded joints between longer rail sections, particularly when they are not supported on anti-friction rollers, in cases where so-called thermite weld joints are cut out, resulting in large welding gaps which must be replaced by flash-butt welded joints, as well as for end welds at temperatures below the normal welding temperature and continuous welded track rails.
To enable the gap between adjacent rail section ends to be reduced after the elements fastening them to the ties have been loosened and thus to prepare for the flash-butt welding with such welding heads, British patent No. 1,294,216, published Oct. 25, 1972, discloses a hydraulic tensioning device for continuous welded rail, which is constituted by a ring-shaped structural unit comprising two longitudinally spaced pairs of rail clamping heads interconnected by tie members extending above and below the rail for rotation about a vertical axis. Short bell-crank levers connect the clamping jaws respectively with hydraulic cylinders and tensioning members extending in the direction of the rail and parallel to a horizontal plane passing through the rail. A manually operated pump delivers hydraulic fluid to the cylinders and when they are operated, the clamping jaws clampingly engage the rail web and, upon additional hydraulic pressure being applied, the clamped ends of the two adjoining rail sections, whose fastening elements have previously been loosened, are pulled together to reduce the gap between the adjacent rail section ends and enable them to be welded together. This device is relatively heavy and may be disassembled. The device is mounted on the rail sections at each welding site, dismounted after use and transported to the next site where it is mounted again and operated by the manually operated hydraulic fluid pump. To enable the device to be readily transported from welding site to welding site, it has been made as small and light as feasible, thus limiting the dimensions of the central space within the ring-shaped unit. Even so, the unit may weigh as much as about 400 kg and is, therefore, difficult to handle, which considerably delays the operations.
A similar, but much lighter and even smaller, rail tensioning device has been disclosed in British patent No. 1,161,307, published Aug. 13, 1969. This device has such small dimensions that its tensioning force suffices only for longitudinally sliding or stretching very short and light rail sections.
European patent No. 132,227, published Jan. 23, 1985, discloses a ring-shaped rail tensioning unit for use in welding together the adjacent ends of rail sections. This unit is designed for longitudinally, vertically and laterally displacing a respective rail section end for centering the same with respect to an adjacent rail section end before the ends are welded together. It is a rather complicated device including a number of servomechanisms and provides a central space holding a shearing device with cutters for removing the weld seam. As the drawing clearly shows, this space is much too narrow to hold a flash-butt welding head.
British patent No. 2,000,829. published Jan. 17, 1979, also discloses a very complicated apparatus for aligning and setting the gap between adjacent rail section ends to be subsequently joined together by a fish plate or welding. There is no room in this apparatus for accommodating a flash-butt welding head so that the pulled-together rail section ends can be joined only in a thermite welding process. This type of rail welding is not only difficult and must be effected manually but it also results in a relatively weak rail joint.